One- and two-component curable compositions are used extensively in composites, coatings, adhesives, sealants and other similar industrial applications. Specific types of one-component curable compositions are epoxy resins and (meth)acrylate resins which are cured upon exposure to radiation, e.g. ultraviolent light, gamma-radiation or electron beam radiation, and/or by the addition of a curing agent. Some specific types of two-component systems are epoxy resins and (meth)acrylate resins which are cured with amines or amino-functional silanes. Such systems generally require tin catalysts to facilitate an expedited cure. But, unfortunately, tin catalysts continue to face increasing environmental scrutiny.
As an alternative to amines or amino-functional silanes, there has been some limited use of mercapto-functional silanes for curing epoxy resins or as adhesion promoters for epoxy resins or (meth)acrylate resin compositions. The amino-functional silane or mercapto-functional silane react with the epoxy resins to form a chemical bond between the silanes and the epoxy resins, and in a subsequent step, cure through hydrolysis and condensation of the silyl group upon exposure to moisture. However, the mercapto-functional silane compounds have the undesirable side effect of a pungent odor which is created by the mercapto groups therein and the high volatility of the mercapto-functional silane.
Other alternatives have been to use epoxy-functional alkoxysilanes and amino-functional alkoxy silanes, but such compounds tend to produce volatile organic compounds (VOC's) or compounds which may be hazardous to humans or to the environment, such as methanol, during cure. These epoxy-functional alkoxysilane and amino-functional alkoxysilanes, which are used as adhesion promoters, may also suffer from less than optimal adhesion to certain metals, such as zinc surfaces due to either labile Si—O-Metal bonds or low levels of Metal-OH groups needed to form the Si—O-Metal bonds.
In the industry, there is a need for improved silane end-capper that may provide for crosslinking of epoxy resins and/or (meth)acrylate resin, either as the only curing mechanisms or as part of a dual cure mechanism, and/or an adhesion promoter to improve adhesion to metal surfaces, especially metal surfaces which do not readily form stable Si—O-Metal bonds between the silyl group and the metal, where these silane end-cappers and adhesion promoters reduce or eliminate the generation of volatile organic compounds during use.